1. Field of the Invention
This invention relates to an automatic compensator for compensating a collimation error due to a twodirectional inclination in surveying instruments such as automatic rotational beam levels and automatic optical plummets and, more particularly, to a device for automatically compensating a collimation error due to inclination of the instument body in two directions, i.e., back-and-forth direction and left-to-right direction by a pendulum mounted with a reflector.
2. Description of the Prior Art
A well-known surveying instrument such as an automatic optical plummet is provided with a device, which includes a reflector mounted at the lower end of a pendulum suspended in the instrument body interior. When the instrument body is inclined in the back-and-forth direction, the collimation axis of the instrument is automatically corrected to a vertical direction by the swing action of the pendulum. In this case, compensation is done for an error due to inclination of the instrument body only in one direction. However, when the instrument body is inclined not only in the back-and-forth direction but also in the left-to-right direction, the errors in these two directions can not be compensated at a time.
Therefore, in the prior art automatic optical plummet, a vertical plane in the back-and-forth direction is first set with respect to a certain direction, then the instrument body is rotated 90.degree., and then a vertical plane in the back-and-forth direction is set again. The intersection between the two vertical planes is obtained to set the true zenith direction. This method is very cumbersome in operation, and it is impossible to directly set the true zenith direction.